Waveguide filter

ABSTRACT

A waveguide filter formed from a substrate (S), which is coated on the upper face with a structured metallic layer (TM) and one or more metallic striplines (ML 1 , ML 2 ), and a component (FB) fitted to the upper face of the substrate (S) and with one side wall of the waveguide filter being formed by the structured metallic layer (TM) of the substrate (S). The other side walls of the waveguide filter are formed by the component (FB), and with the waveguide filter having input and output points for coupling the electromagnetic waves carried in the stripline (ML 1 , ML 2 ) to the waveguide filter, and vice versa.

This application claims priority to International Patent Application No.PCT/DE2003/002552, filed Jul. 30, 2003, designating the United States ofAmerica, and German Application DE 102 43 670.3-35, filed Sep. 20, 2002,the disclosure(s) of which is (are) expressly incorporated by referenceherein.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a waveguide filter.

Waveguide filters are conventional components for microwave andmillimetric wave technology. This filter type normally has relativelyhigh resonator Q-factors and narrow electrical tolerances for thepassband and cutoff band. Waveguide filters are distinguished by highstop-band attenuations and a low insertion loss. Waveguide filters arepreferably used where it is no longer possible to use planar filtersowing to stringent requirements for the electrical tolerance accuracyand the Q-factor.

An arrangement for frequency-selective suppression of radio-frequencysignals is known from German Application DE 197 57 892 A1. Thearrangement in this case has a baseplate with a first and a secondsubstrate surface, each having a coupling connection and each having anelectrically conductive panel. A shroud which is arranged over thebaseplate, together with the electrically conductive panel, forms ahollow chamber which acts as a cavity resonator. The cavity resonatoracts as a high-pass filter, so that the only frequencies which canpropagate are those which are higher than a cutoff frequency that isdetermined by the geometric dimensions of the cavity resonator.

A further known filter is known from U.S. Pat. No. 6,236,291 B1. Ahousing which, together with the upper face of the substrate, forms acavity, is arranged on the upper face of a substrate whose lower face iscompletely metallically coated. A dielectric panel which acts as adielectric filter is arranged in this cavity.

FIG. 1 shows a further possible arrangement. The illustration shows theintegration of a waveguide filter in a planar circuit according to theprior art. The arrangement comprises a substrate S which has a firststripline ML1 and a second stripline ML2, for example a microstripline,on the upper face. The first stripline ML1 is in this case used forinputting the transported electromagnetic wave into the waveguide filterHF, and the second stripline ML2 is used for outputting the wave fromthe waveguide filter HF. Input and output points are provided at the twoends of the filter for inputting/outputting the signal from/to thestripline, in order to change the signal from the mode which canpropagate on the stripline to the waveguide mode which can propagate inthe filter, and vice versa.

These coupling points are formed at both ends of the filter from thestriplines ML1, ML2, the substrate S, the shielding-cap SC, the viaholes VH, the rear aperture face body RM and the baseplate TP with thecap DB.

The striplines ML1, ML2 each end underneath a shielding SC, which isused to prevent radiated emission of electromagnetic waves to thesurrounding area. Rear-face metallization RM, which has an aperture DBin the area of the shielding cap, is located on the lower face of thesubstrate S. A metallic baseplate TP is arranged on the lower face ofthe substrate and likewise has an aperture DB in the area of theshielding cap, so that the two apertures in the rear-face metallizationof the substrate and in the baseplate TP are aligned with one another.The waveguide filter HF is screwed to this baseplate TP, with each ofthe openings in the waveguide filter being connected to the aperturesDB.

An electromagnetic wave passes from the first stripline ML1 through thesubstrate S and the aperture DB into the waveguide filter HF. Theelectromagnetic wave is then passed from the waveguide filter HF throughthe apertures DB to the second stripline ML2.

One disadvantage of the integration of a conventional waveguide filterin a stripline environment (for example on printed circuits) is the highcosts associated with this which, until now, have prevented widespreaduse of this principle. The cost drivers in this area are the largenumber of manufacturing steps and components, and the necessity to fitcomponents on the front face and rear face of the substrate.

The waveguide junction requires a precision-manufactured, mechanicallyaccurately positioned shielding cap SC. The metallization on both facesof the substrate S must be structured with a small offset between theconductor track patterns on the lower face and upper face. The apertureDB in the baseplate must be produced in an additional manufacturingstep. The substrate S must be connected to the baseplate TP conductivelyand accurately positioned. A shielding cap, which must be produced as aseparate component, must be fitted to the substrate S conductively andaccurately positioned.

The waveguide filter HF normally comprises two parts (a waveguide filterlower part with three side walls of the waveguide filter and a coverpart as a fourth side wall of the waveguide filter) which must beproduced separately and must first of all be joined. The joined filtermust then be attached to the lower face of the baseplate, such that itis accurately positioned.

Further disadvantages result from the fact that the waveguide filternormally has a number of components (shielding cap, baseplate, waveguidefilter) and that this type of implementation occupies a large amount ofspace.

The object of the invention is to provide a waveguide filter which canbe adapted to a printed circuit board easily, at low cost and in aspace-saving manner.

According to the invention, the waveguide filter is formed from asubstrate, coated on the upper face with a structured metallic layer andone or more metallic striplines, and a component fitted to the upperface of the substrate. One side wall of the waveguide filter is formedby the structured metallic layer of the substrate, and the other sidewalls of the waveguide filter are formed by the component. The waveguidefilter has input and output points for coupling the electromagneticwaves carried in the stripline to the waveguide filter, and vice versa.

One advantage of the waveguide filter according to the invention is thatessentially includes a single component which can be produced easily andat low cost and is fitted to the upper face of an appropriatelypreviously structured substrate. The waveguide filter is, in this case,not formed by the component or the substrate per se, but only by thearrangement of the two elements with respect to one another according tothe invention.

The component can advantageously be a surface mounted device. A largenumber of the components used on a printed circuit board are normallysurface mounted devices. The waveguide filter surface mounted deviceaccording to the invention can expediently be included in themanufacturing process. The assembly can be populated from just one side.This results in further advantages in terms of manufacturing costs andtime.

The component, which is also referred to as the filter upper part,advantageously has a conductive surface and may, for example, beproduced from metal or metallized plastic, with the latter resulting infurther advantages in terms of production costs and weight. The filterupper part is advantageously conductively connected to the substrate, inparticular with the filter upper part being soldered or conductivelyadhesively bonded to the substrate.

In one advantageous embodiment of the invention, the filter upper partis structured on the side wall which is opposite the upper face of thesubstrate (that is to say the substrate face to which the filter upperpart is attached). This structure can then be predetermined, dependingon the desired waveguide filter characteristics. The cross section ofthe waveguide filter can advantageously be chosen to correspond to theradio-frequency signal to be filtered.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention as well as further advantageous embodiments will beexplained in more detail in the following text with reference todrawings, in which:

-   -   FIG. 1 shows a waveguide filter, fitted to a substrate,        according to the prior art,    -   FIG. 2 shows a plan view of the filter upper part with a        structured internal surface,    -   FIG. 3 shows a longitudinal section through the filter upper        part along the section line A-A′ in FIG. 2,    -   FIG. 4 shows a plan view of the metallized layer on the upper        face of the substrate, and    -   FIG. 5 shows a cross section through an arrangement according to        the invention of a waveguide filter comprising a substrate and a        filter upper part, along the section line B-B′ in FIG. 2 and        FIG. 4.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 2 shows a plan view of the filter upper part with a structuredinner surface. At each of its opposite ends, the filter upper part FBhas an opening OZ through which the microstriplines (see FIG. 4 and FIG.5) are passed into the waveguide filter. The filter upper part FB isessentially U-shaped (see FIG. 3) and has a structure SK in theinterior. The structure SK is in this case advantageously chosen tocorrespond to the desired waveguide filter characteristics.

Manufacturing methods such as milling or plastic injection molding canbe used to produce mechanically high-precision structures SK, so thatthe waveguide filter also, in a corresponding manner, has only minorelectrical tolerances for the input and filter function.

Furthermore, the filter upper part FB advantageously has acircumferential web ST (FIG. 2 and FIG. 3). In the waveguide filter,this web ST is seated directly on the metallized upper face of thesubstrate (not shown). This web ST is expediently adapted for therespective joining method that is used. The conductive solder or theconductive adhesive can be distributed in the space formed between thefilter upper part and the substrate when they are joined together, thusensuring an optimum connection.

The web ST can expediently be adapted such that, for example when thejoining method is “soldering”, the surface tensions which occur in thesolder during the soldering process can be used to ensure that thecomponent FB is positioned exactly on the metallically structured layerillustrated in FIG. 4 during the soldering process.

FIG. 3 shows a section illustration of the filter upper part along thesection line A-A′ in FIG. 2. The illustration shows the essentiallyU-shaped filter upper part FB with the internal structure SK. Thestructure SK is in this case illustrated only by way of example. Otherstructure forms are, of course, also possible depending on theapplication.

FIG. 4 shows a plan view of the metallized upper face of the substrate,to which the filter upper part can be fitted in order to form thewaveguide filter according to the invention. In this case, ML1, ML2denote the striplines, and TM denotes the metallization, which forms onewall of the waveguide filter in the arrangement according to theinvention. The striplines ML1, ML2 may, for example, be microstriplinesand are used for inputting and outputting the electromagnetic waves intoand out of the waveguide filter.

FIG. 5 shows a section illustration along the section line B-B′ fromFIG. 2 and FIG. 4 for a waveguide filter arrangement according to theinvention. The waveguide filter HF is formed by the filter upper partFB, as illustrated in FIG. 2, being fitted with high-precision to themetallized upper face TM of the substrate S, as illustrated in FIG. 4.

The striplines ML1, ML2 which are formed on the upper face of thesubstrate S lead from the outside into the internal area of thewaveguide filter HF. The metallization TM on the upper face of thesubstrate S forms the fourth wall, according to the invention, of thewaveguide filter HF. The other side walls of the waveguide filter HF areformed by the filter upper part FB.

1. A waveguide filter comprising a substrate (S), coated on at least aportion of upper face with a structured metallic layer (TM). at leastone metallic stripline for carrying electromagnetic waves, and acomponent fitted to the upper face of the substrate (S), wherein oneside wall of the waveguide filter is formed by the structured metalliclayer (TM) on the substrate (S), and wherein other side walls of thewaveguide filter are formed by the component (FB); said waveguide filterhaving input and output points for coupling the electromagnetic wavescarried between the at least one metallic strip lines and an internalportion of the waveguide filter.
 2. The waveguide filter as claimed inclaim 1, wherein the component (FB) is a surface mounted device.
 3. Thewaveguide filter as claimed in claim 2, wherein the component (FB) has acircumferential web (ST) which rests on the structured metallic layer(TM) on the upper face of the substrate (S).
 4. The waveguide filter asclaimed in claim 1, wherein a cross section of the component (FB) ischosen in accordance with predeterminable filter characteristics of thewaveguide filter (HF).
 5. The waveguide filter as claimed in claim 1,wherein a side wall of the component (S) which is opposite the upperface of the substrate (S) has a structure (SK) which can bepredetermined for corresponding appropriate filter characteristics.
 6. Awaveguide filter, comprising: a substrate at least partially coated witha structured metallic layer, a surface mounted device fitted on saidstructured metallic layer and forming a plurality of surfaces of saidwaveguide fitter, at least one metallic stripline formed on saidsubstrate for carrying electromagnetic waves.
 7. The waveguide filter asclaimed in claim 6, wherein the component (FB) has a circumferential web(ST) which rests on the structured metallic layer (TM) on the upper faceof the substrate (S).
 8. The waveguide filter as claimed in claim 6,wherein a cross section of the component (FB) is chosen in accordancewith predeterminable filter characteristics of the waveguide filter(HF).
 9. The waveguide filter as claimed in claim 6, wherein a side wallof the component (S) which is opposite the upper face of the substrate(S) has a structure (SK) which can be predetermined for correspondingappropriate filter characteristics.
 10. The waveguide filter as claimedin claim 2, wherein a cross section of the component (FB) is chosen inaccordance with predeterminable filter characteristics of the waveguidefilter (HF).
 11. The waveguide filter as claimed in claim 3, wherein across section of the component (FB) is chosen in accordance withpredeterminable filter characteristics of the waveguide filter (HF). 12.The waveguide filter as claimed in claim 2, wherein a side wall of thecomponent (S) which is opposite the upper face of the substrate (S) hasa structure (SK) which can be predetermined for correspondingappropriate filter characteristics.
 13. The waveguide filter as claimedin claim 3, wherein a side wall of the component (S) which is oppositethe upper face of the substrate (S) has a structure (SK) which can bepredetermined for corresponding appropriate filter characteristics. 14.The waveguide filter as claimed in claim 4, wherein a side wall of thecomponent (S) which is opposite the upper face of the substrate (S) hasa structure (SK) which can be predetermined for correspondingappropriate filter characteristics.